1. Field of the Invention
The present invention relates to a die abnormality prediction system, a press machine provided with the same, and a die abnormality prediction method.
2. Description of Related Art
Regarding a press machine that performs stamping using a die, there is a conventionally known method for detecting an abnormality in the die. For example, Japanese Patent No. 4372458, Japanese Patent No. 4959360, and Masuaki MURAO, et al., “Improving Quality and Productivity through Newly Developed Acoustic Emissions Technology”, Denso technical review, Vol. 9, No. 1, 2004, p. 92 to 99 disclose methods for detecting an abnormality during deformation processing, using an acoustic emission (AE) sensor that detects elastic waves generated from a processing portion of the die.
Japanese Patent No. 4372458, and Masuaki MURAO, et al., “Improving Quality and Productivity through Newly Developed Acoustic Emissions Technology”, Denso technical review, Vol. 9, No. 1, 2004, p. 92 to 99, disclose an abnormality determination and evaluation method for determining a failure regarding a nick in a stamped product, and failures regarding a damage and an abrasion to a die, using elastic waves detected by an AE sensor.
Specifically, according to the method disclosed in Japanese Patent No. 4372458, abnormality determination is performed using, out of elastic waves detected by the AE sensor, first elastic waves that are emitted during a processing step that is performed immediately before an upper die is brought into contact with a lower die, second elastic waves that are emitted during a processing step that is performed when the upper die is brought into contact with the lower die, and third elastic waves that are emitted during a processing step performed after the upper die has brought into contact with the lower die. According to the method disclosed in the aforementioned Japanese Patent No. 4372458, a failure regarding a nick in a stamped product is determined based on the integrated value of the first elastic waves, and a failure regarding a damage to the die is determined based on the maximum value of the second elastic waves, and a failure regarding an abrasion to the die is determined based on the integrated value of the third elastic waves.
Japanese Patent No. 4959360 discloses a method for detecting an abnormality in deformation processing based on a value (power) obtained by analyzing the frequencies of elastic waves detected by an AE sensor.
Specifically, according to the method disclosed in Japanese Patent No. 4959360, the output signal from the AE sensor is also subjected to time-series frequency analysis per unit time, and power corresponding to the frequency is calculated in time-series per unit time. According to the method disclosed in Japanese Patent No. 4959360, an abnormality in deformation processing is detected by obtaining power differences between an obtained calculation value and reference data indicating time-series variations in the power corresponding to a frequency during normal deformation processing, and then using an integrated power difference per unit time obtained by calculating the sum of the power differences corresponding to the frequencies.
As disclosed in the above-described Japanese Patent No. 4372458, Japanese Patent No. 4959360, and Masuaki MURAO, et al., “Improving Quality and Productivity through Newly Developed Acoustic Emissions Technology”, Denso technical review, Vol. 9, No. 1, 2004, p. 92 to 99, it is possible to detect an abnormality in stamping such as abrasion to a die by detecting elastic waves generated during stamping, using an AE sensor.
As described above, it is possible to determine whether or not an abnormality has occurred, using elastic waves detected by the AE sensor. However, in cases where processing is performed using a press machine or the like, even if a countermeasure such as die maintenance or die replacement is taken immediately after an abnormality is detected, there is the possibility of defective products being produced until the countermeasure is complete. As a result, it becomes necessary to perform a product test to determine whether or not products are defective and to discard defective products, and thus an additional cost is generated.
Therefore, it is important to determine when in the future an abnormality will occur in stamping, i.e., to determine the current state of stamping and to predict an abnormality that might occur in the future. By predicting the occurrence of an abnormality in such a manner, it is possible to promptly take a countermeasure such as die replacement, and it is therefore possible to prevent defective products from being wastefully produced.